In general, in the conventional extruding machines, a plastic such as a thermoplastic resin is melted while being transported by a screw conveyor within a closed cylinder and the molten plastic is extruded toward a die having a predetermined opening and ejected through the opening to form a plastic product having a desired shape.
FIG. 3 shows a conventional plastic molding machine of the type described above. A hopper for feeding a predetermined plastic powder into the cylinder of an extrusion machine 1 is mounted thereon and with the interior of the extrusion machine 1 has a screw conveyor 4 for transporting the plastic powder supplied from the hopper 2 toward a head 3 and a heater (not shown) for melting the plastic powder being transported by the screw conveyor 4 toward the ejection opening of the head 3.
The extrusion opening of the head 3 of the extrusion machine 1 is connected to an L-shaped feed pipe 5 and a feeding opening 7 of a die 6 for forming,for example, tubular plastic products is detachably connected to the leading end of the feed pipe 5. An annular emerging opening 9 for emerging the molten plastic 8 so as to form a tubular plastic product is formed through the upper surface of the die 6. Furthermore, defined at the lower portion of the die 6 is an air injection opening 11 for expanding and maintaining the shape of the molded product in the form of a tube. An annular cooling air supply device 12 is disposed upwardly of the ejection opening 9 of the die 6 adjacent to the upper portion of the die 6. The cooling air supplied from a blower (not shown) is injected through the ejection opening 9 into the tubular plastic product 8, thereby cooling the same.
A plurality of guide rollers 13 are disposed upwardly of the cooling air supply device 12 so that the cooled tubular plastic product can be gradually made into the form of a flat laminated sheet. Disposed upwardly of the uppermost guide roller pair is a pair of pinch rollers 14 for pulling up the flatly laminated plastic product 8. A winding roller 15 for winding the flatly laminated plastic product 8 is disposed at the downstream side of the uppermost guide roller pair 13.
With the conventional plastic forming machine with the above-described construction, the predetermined plastic powder 8 is fed into the extrusion machine 1 through the hopper 2 and is melted while being transported by the screw conveyor 4. Thereafter, the molten plastic is forced to emerge through the opening of the head 3 and then fed into through the feed pipe 5 into the inlet opening 7 of the die 6. The die 6 forms the molten plastic 8 into a tubular shape, which is discharged from the emerging opening 9 upwardly. In this case, the air is fed into the die 6 through the air supply opening 7 and injected at a predetermined pressure level through the air injection opening 11 into a tubular plastic product 8 so that the product 8 is expanded and maintained in a predetermined shape. The emerged plastic product 8 is cooled by the cooling air injected from the cooling air supply device 12 so that the plastic product 8 is cooled and then gradually laminated by the guide rollers 13 into a flat shape. The laminated plastic product 8 thus formed is pulled up by the pinch roller pair 14 and then wound around the winding roller 15.